An inkjet recording system is a recording method that performs recording of pictures, characters and the like (hereinafter called “images”) by causing tiny droplets of inks to adhere a recording medium such as paper in accordance with one of various operation principles and at the same time, causing the solvent component of each ink to penetrate into the recording medium or to evaporate such that its colorant component is allowed to deposit on the recording medium. The inkjet recording system is characterized in that it is excellent in high-speed printing, low operating noise and the applicability for the recording of a wide variety of patterns; and it also can readily perform multicolor recording, and requires neither development nor image fixing.
In particular, multicolor inkjet recording systems are rapidly finding increasing utility as image recording systems for various information equipment in recent years, because images formed by multicolor inkjet recording can provide records favorably comparable with multicolor prints by the form-plate-dependent printing or images by color photography and moreover, and have a merit that multicolor inkjet recording is lower in printing cost than usual printing techniques or photographic techniques when the number of copies or prints to be made is small. Accordingly, the use of multicolor inkjet recording is spreading to fields where the recording of full color images is needed, for example, such as the output of image designs in the design world, the production of color block copies in the printing field, said color block copies being required to have quality as high as photographic images, and samples of frequently-replaced billboards and merchandises. Owing to the wide spread of personal computers and digital still cameras in recent years, there is also an increasing number of occasions to output photographic images by inkjet printers at home.
Under the current circumstances, however, images recorded by inkjet printers undergo significant color fading or discoloration by acidic gas in the atmosphere and light in comparison with the images of multicolor prints by form-plate-dependent printing or color photographs, and therefore, are not suited for the long-term storage of the images. Accordingly, there is a very strong demand for the prevention of color fading or discoloration of images, and numerous proposals have been made to date for making improvements in this respect.
To make improvements in gas fastness, for example, Patent Document 1 discloses recording media with thioether compounds incorporated therein, Patent Document 2 discloses recording media with hydrazide compounds incorporated therein, and Patent Documents 3 and 4 disclose recording media with thiourea derivatives, thiosemicarbazide derivatives, thiocarbohydrazide derivatives or the like incorporated therein. Further, Patent Document 5 discloses recording media each of which contains, in combination, one of thiourea derivatives, thiosemicarbazide derivatives and thiocarbohydrazide derivatives and one of iodine, iodides, dithiocarbamic acid, thiocyanate salts and thiocyanate esters.
As methods for making improvements in light fastness, on the other hand, Patent Document 6, Patent Document 7 and Patent Document 8 disclose recording media with phenolic antioxidants or benzophenone or triazole ultraviolet absorbers incorporated therein.
In addition, recording media containing hindered amine compounds are proposed in Patent Document 9, and those containing hydrazide compounds are proposed in Patent Document 10.
Furthermore, Patent Documents 11 and 12 disclose recording media with gas fastness and light fastness improved by incorporating ascorbic acid, erythorbic acid or sodium erythorbate in ink-receiving layers, and Patent Documents 13, 14 and 15 disclose recording media with gas fastness and light fastness improved by incorporating flavonoid in ink-receiving layers.
However, these conventionally-known methods for providing recording media with gas fastness and/or light fastness have not fully brought about their effects, and are not considered to be sufficient for the improvement of the properties. Moreover, many of the above-mentioned compounds are insoluble in water so that they cannot be added to water-based coating formulations, and even in the case of water-soluble compounds, it is difficult to actually apply them to recording media due to a problem that they deteriorate water resistance and the migration of images at high temperature and high humidity.    Patent Document 1: JP-A-01-115677    Patent Document 2: JP-A-61-154989    Patent Document 3: JP-B-04-034953    Patent Document 4: JP-A-07-314883    Patent Document 5: JP-A-08-025796    Patent Document 6: JP-A-57-074192    Patent Document 7: JP-A-57-087989    Patent Document 8: JP-A-60-072785    Patent Document 9: JP-A-61-146591    Patent Document 10: JP-A-61-154989    Patent Document 11: JP-A-07-195824    Patent Document 12: JP-A-08-015077    Patent Document 13: JP-A-2001-071627    Patent Document 14: JP-A-2001-139850    Patent Document 15: JP-A-2001-301315